Vacuum coating process and apparatus therefor



Feb. 5, 1952 G, BANCRQFT 2,584,660

VACUUM COATING PROCESS AND APPARATUS THEREFOR Filed Sept. 24, 1949 IN VEN TOR.

GEO 65 H BANCROFT ATTORNEYS Patented F ch. 5, 1 952 VACUUM COATINGPROCESS AND APPARATUS THEREFOR George H. Bancroft, Rochester, N. Y.,assignor, by mesne assignments, to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Application September 24, 1949, SerialNo. 117,598

' 9, Claims. (01. 117-93) This invention relates to the art of coatingmaterials under vacuum and is particularly concerned with coatingmaterials with metal vapors evolved by thermal evaporation under vacuum.

It is an object of this invention to provide improved apparatus forcoating materials under vacuum.

It is a further object of the invention to provide means forcontinuously coating strip material with metal.

It is a further object to provide metal coating apparatus not subject tobreakdown during operation.

Another object of the invention is to provide means for subjectingcoating metal to thermal evaporation in a progressive manner withoutinterrupting the coating process.

Another object of the invention is to provide an improved process forthermally evaporating coating metal under vacuum.

Another object of the invention is to obviate the necessity of employingphysical supporting means to laterally support molten metal beingevaporated under vacuum.

Another object of the invention is to provide metal coating apparatusnot subject to crucible failure.

Other objects will be apparent from the drawings, description andclaims. 7

Of the drawings: r

Fig. l is a view in elevation and partly in section of vacuum coatingapparatus constituting a preferred embodmient of the invention;

Fig. 2 is an enlarged fragmentary view in elevation of the coater shownin Fig. 1 with particular reference to the source;

Fig. 3 is a fragmentary view in elevation of a modified source; and

Fig. 4 is a fragmentary view in elevation partly broken away and insection of a further modified source, including a crucible and a chargeof metal having the configuration assumed by the metal when melted inaccordance with this invention.

The invention is best understood by reference to preferred apparatusembodying the invention as shown in Fig. l. The preferred apparatuscomprises an evacuable chamber Ill formed by wall means consisting ofbase II and bell dome I2. Bell dome I2 is movable into and out ofsealing engagement with base plate II, gasket I3 providing a gas-tightseal when dome I2 is in position on base plate I I.

Chamber I communicates with pumping means I3 through conduit I5, pumpingmeans I3 comprising any suitable vacuum pumping ar- Y generatorrangement for evacuating chamber III to a pressure below about micronsHg. and preferably below 10 microns Hg. The pumping means dosirablycomprises a plurality of diffusion pumps backed by a mechanical pump inthe manner well known in the art.

The source for thermally evaporating coating metal in chamber I0comprises induction heating coil I6 connected by leads I1, I! throughbase plate II to current generator I8.

Coil I6 preferably comprises a plurality of turns of copper or othermetal tubing defining a central opening in which an alternatingelectromagnetic field is established when coil I6 is energized by I8.Coil I6 is rigidly supported in generally vertical position insidechamber I0 by post 20 which is mounted on base plate II.

Generator I8 adapted to energize coil I6 is an alternating currentgenerator supplying current having a frequency of about 5 to 50kilocycles per second.

Extending through base plate II in vertical alignment with coil I6 isadjustable feed member 2I comprising a threaded shank 22 extendingthrough a threaded opening in base plate II,

knurled head 23 and handle 25, and clamping collar 26. Collar 26 isadapted to hold and vertically support a rod 21 of coating metal with anend portion of rod 21 extending upwardly into coil I6. In the interestof simplicity, a manually operable feed has been illustrated but powerdriven feeds and automatic controls may be added.

Driven rolls 28 and 30 are rotatably supported in spaced relation inchamber I0 on support members 3|, 3|. Rolls 28 and 30 carry stripmaterial 32 to be coated. Rolls 28 and 30 are controllably rotated byrotatable shafts 33 and 35 respectively geared with rolls 28 and 30 andextending downwardly through gland packings (not shown) in base plate IIto suitable driving means (not shown). Rolls 28 and 36 are arranged toroll and unroll strip material 32 in proximity to the source.

In a modified form as shown in Fig. 3, the source employed in theapparatus embodying the invention comprises a refractory crucible 36mounted in and supported by coil I6. Crucible 36 is provided with anopening 31 through the bottom thereof, the opening being adapted toaccommodate rod 21 extending upwardly into coil I6. The lower portion ofcrucible 36 desirably extends downwardly out of coil I6 whereby thelower portion is out of the electromagnetic field established in coili=3 when coil 18 is energized by generator it.

In a further modification of the source as illustrated in Fig. 4,crucible 3'! is positioned completely within coil l6 and is adapted forholding a body of coating metal 323 for batchwise operation, theconfiguration assumed by the coating metal when molten and under theinfluence of the electromagnetic field in the coil being shown in Fig.l.

In a preferred coating process embodying the invention and employing theapparatus shown in Fig. l, strip material 32 to be coated is mounted onroll 28 and fed across to roll 30. The strip material may be any desiredsheet material such as plastic film, textile sheeting, paper or thelike.

A rod 2'1 of coating metal is clamped in collar 26 with an end of therod extending upwardly into coil 58 at the approximate center of thecoil. Rod 2? is of any desired thermally evaporable coating metal suchas aluminum, copper, silver, chromium and the like depending upon thematerial being coated and the coating desired.

Dome is then lowered into sealing engagement with base plate ii andpumps (3 are put into operation. The chamber is evacuatedto a pressureeffective to cause the desired evaporation of coating metal when molten.*t is usually desirable to carry out the coating process at pressuresbelow about 10 microns Hg. although pressures as high as 160 microns Hg.can be employed. ii desired, the apparatus is first employed to degasthe material to be coated, degassing being effectively accomplished byrepeatedly rolling and unrolling the strip material in the evacuatedchamber before the actual coating is begun. If desired, however,degassing can be effected in the chamber by suitable glow dischargemeans or the material can be degassed in a separate chamber.

Coil i6 is then energized by generator l5, set- "11' up a localizedalternating electromagnetic in the coil, the field having a frequency of50 liilccycles per second. The end portion of rod 2? extending into thefield is inductively melted with the remainder of the rod outside thefield re naining solid. The field, at the relatively low frequenciesemployed, electromagnetically compacts and laterally supports the moltenportion of the rod. The solid portion of the rod provides verticalsupport for the molten end portion and I have found that no physicalsupporting means are necessary for lateral support;

The molten end portion under the influence oi the electromagnetic ileldhas the appearance of a glowing, wavering finger of molten metal havinga rounded tip and it is maintained in the coil without use of a crucibleor other container means. Further, the inoiten tip is self-cleaningsince any oxide skin forming on the tip flows down the sides of the endportion to a cooler zone.

Rolls 28 and 3% are thereupon actuated to roll and unroll the stripmaterial to be coated, the strip material bein in proximity to thesource during passage between the rolls whereupon metal vapors evolvedfrom the rod of coating metal condense on the sheet material. The rateof rotation of the rolls is controlled at the rate necessary to deposita coating of the desired thickness on the sheet material during passagebetween the rolls, coat-ing speeds of from to 30 feet per minute orhigher being commonly employed.

As the end of the rod of coating metal evaporates away, the rod isprogressively advanced wardly into the electromagnetic field by turningfeed member 2| which is operable from outside the evacuated chamber. Thecoating process embodying this invention is operated continuously untilthe entire roll of sheet material is coated. By supporting the moltenmetal electromagnetically, it is possible to progressively introduceadditional coating metal into the evaporating zone without employingelaborate feed means or interrupting the process by opening the chamber.

When the sheet material is coated to the desired thickness, the coil canimmediately deenergized whereupon the molten tip of the coating rodcollapses and flows down the sides or the rod, but more desirably theileld strength is gradually decreased until the molten tip begins tosolidify.

If desired the process can be carried out employing the modified sourceshown in Fig. 3. In this embodiment of the inventi n, a crucible oirefractory material such as carbon, graphite, mica, alundum or the likeis placed 'n the coil, preferably with the lower portion of the crucibleextending downwardly out of the coil. When a rod of coating metal isemployed, as in Fig. 3. the crucible is provided with an opening throughthe bottom of a diameter just suflicient to accommodate the rodextending upwardly into the coil.

In the process embodying the invention, the molten portion of the rod issupported laterally by the electromagnetic field and is out or lateralcontact with the crucible. This greatly minimizes alloying of thecoating metal with the crucible which is a common cause of cruciblefailure. The crucible serves to catch the molten metal when the coil isdeenergized and the molten end or the rod collapses, the high viscosityoi the molten metal preventing any substantial leakage of metal out ofthe crucible opening around the rod.

By maintaining the lower portion of the crucible out or" the coil, asshown in Fig. 3, the crucible bottom is relatively cool and the moltenmetal quickly solidifies. Furthermore, the crucible bottom is notweakened by prolonged heatr and the tendency of the crucible bottom tobreak under the impact of the collapsing metal is minimized.

In resuming operation of apparatus employing the source shown in Fig. 3,it is not necessary to remove the fused metal from the preceding run,Elie rod is merely advanced, pulling the crucible up into the coil. Asthe metal in the bottom oi the crucible melts, the crucible graduallyslides down to its original position and the molten portion is compactedaway from the crucible walls by the electromagnetic field.

In a further modification of the invention. employing a source as shownin Fig. i, arefractory crucible having a closed bottom is employed. Thisform of source is particularly suitable for coating a plurality ofindividual articles held in the charm bar by suitably modified holdingmeans, since a batchwise operation is necessary and a single charge ofcoating metal in the crucible is suiiicient for several single coatingoperations in many cases.

When such a source is employed, the electromagnetic field laterallycompacts and supports the molten metal in aconfiguration correspondinggenerally to that shown in Fig. 4. The molten metal is thus out ofsubstantial contact with the crucible walls and crucible life isextended many times the normal crucible life encountered when the moltenmetal is in direct contact with the crucible walls. As in the previouslydescribed embodiment, any oxide skin or other material gathering on themolten body of metal flows down to the bottom of the crucible leaving amaximum evaporating surface.

In carrying out the process of this invention, field frequencies of from5 to 50 kilocycles have been found to be most desirable althoughsomewhat lower and somewhat higher frequencies can be employed,generally with less efficacious results. At frequencies of the order of100-500 kilocycles or higher, such as are commonly employed in highfrequency induction heating, the electromagnetic field strength is noteffective to laterally compact and support the molten metal out ofcontact with the crucible.

The invention is applicable for coating a variety of articles undervacuum including lenses, and other optical goods, costume jewelry andthe like and is particularly adapted for coating sheetmaterial such asfoil, plastic films such as cellulose acetate and the like, textilematerial of all kinds, paper, leather and the like.

The invention provides simple and effective apparatus for metal coatingunder vacuum and particularly for continuous coating where a largeamount of coating metal is required over a prolonged period of time. Bymeans of the invention, metal coatings of a variety of metals includingaluminum, silver, gold and the like are readily obtained and it isnotable that copper coatings are entirely feasible by means of thisinvention whereas copper does not lend itself to many conventionalcoating processes.

While the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that the processes and apparatus embodying the invention maybe varied or modified within the spirit and scope of the invention asset forth in the drawings and description and as defined in the appendedclaims.

What I claim is:

1. Vacuum coating apparatus comprising in combination wall meansdefining an evacuable chamber, vacuum pumping means communicating withsaid chamber, source means for establishing in said chamber a localizedalternating electromagnetic field effective to vaporize coating metaland having a frequency of 5 to 50 kilocycles per second, said sourcemeans comprising an induction heating coil in said chamber with the axisof said coil substantially vertical and an alternating current generatorconnected to said coil and adapted to supply to said coil alternatingcurrent having a frequency of 5 to 50 "kilocycles per second, supportingmeans adapted to engage and support a rod of coating metal ofsubstantial length, said supporting means being below and generally invertical alignment with said coil and being constructed and arranged tohold said rod with an end portion of said rod extending into said coil,rod feeding means operable from outside said chamber for progressivelyadvancing said rod into said coil as said end portion of said rodevaporates, and holding means in said chamber for disposing material tobe coated in proximity to said source means.

2. Vacuum coating apparatus comprising in combination wall meansdefining an evacuable chamber, vacuum pumping means communicating withsaid chamber, source means for establishing in said chamber a localizedalternating electromagnetic field effective to vaporize coating metaland having a frequency of 5 to 50 kilocycles per second, said sourcemeans comprising an induction heating coil disposed in said chamber withthe axis of said coil substantially ver-- tical and current supplyingmeans for energizing said coil at a frequency of 5 to 50 kilocycles persecond, supporting means for a rod of coating metal, said supportingmeans being positioned below and in generally vertical alignment withsaid coil and being constructed and arranged to hold said rod with anend portion of said rod extending into said coil, crucible means in saidchamber in generally vertical alignment with said coil and saidsupporting means, said crucible having an opening through the bottomthereof sufiicient to accommodate said rod with said rod extending fromsaid support means upwardly into said coil through said opening, rodfeeding means operable from outside said chamber for progressivelyadvancing said rod into said coil as said end portion of said rodevaporates, and controllable means in said chamber for rolling andunrolling sheet material being coated in coating relation to said sourcemeans.

3. Vacuum coating apparatus comprising in combination wall meansdefining an evacuable chamber, a portion of said wall means beingmovable into and out of sealing relation with the remainder of said wallmeans for access into said chamber, vacuum pumping means communieatingwith said chamber, source means for establishing in said chamber alocalized alternating electromagnetic field effective to inductivelyheat and vaporize coating metal and having a frequency of 5 to 50kilocycles per second, said source means comprising an induction heatingcoil disposed in said chamber with the axis of said coil substantiallyvertical and current supplying means connected with said coil and beingadapted to energize said coil with alternating current having afrequency of 5 to 50 kilocycles per second, refractory crucible meansdisposed in said coil and supported by said coil for holding a body ofcoating metal to be vaporized in said field, and controllable means forrolling and unrolling sheet material in said chamber in coating relationto said source means, said controllable means comprising paired rollermeans and means for driving said roller means.

4. Vacuum coating apparatus comprising in combination a gas-tightchamber, means for evacuating said chamber, means for supporting a bodyof vaporizable coating metal in said chamber in proximity to material tobe coated, means in said chamber for holding material in position to becoated, means for inductively melting at least a portion of said body ofmetal and for electromagnetically compacting and laterally supportingsaid portion While it is molten, the lastsaid means including aninduction heatin coil positioned with the axis of said coilsubstantially vertical and with said coil disposed around at least saidportion of said body of metal and means for'supplying to said coil analternating current having a frequency of 5 to 50 kilocycles per second,

5. Vacuum coating apparatus comprising in combination a gas-tightchamber adapted to be evacuated, means for supporting a rod of metal ofsubstantial length vertically in said chamber, coil means in saidchamber, means connected to said coil means for supplying current havinga frequency of 5 to 50 kilocycles per second to said coil means, saidcoil means being disposed with th axis of said coil means substantiallyvertical and being arranged to surround at least an end portion of saidrod, means in said chamber for holding material in position to becoated, and means for advancing said rod into said coil means as metalevaporates from said end portion surrounded by said coil means.

.6. Vacuum coating apparatus comprising in combination wall meansdefining an evacuable chamber, means for evacuating said chamber, coilmeans for establishing in said chamber a localized alternatingelectromagnetic field efiective to vaporize coating metal, meansconnected to said coil means for supplying current having a frequency of5 to 50 kilocycles per second to said coil means, the axis of saidcoilmeans being substantially vertical, support means for holding a rod ofcoating metal with an end portion of said rod extending substantiallyvertically into said coil means and being surrounded by said coil means,means in said chamber for holding material in position to be coated, andmeans operable from outside said chamber for advancing said rod intosaid coil means as said end portion evaporates.

7. In a coating process in which coating metal is thermally evaporatedunder vacuum, th steps which comprise inductively melting at least aportion of a body of coating metal, subjecting said molten portion tovacuum effective to cause evaporation of said portion, and substantiallythroughout said evaporation subjecting said molten portion to analternating electromagnetic field having a frequency of 5 to 50kilocycles per second and thereby electromagnetically compacting andlaterally supporting said portion of said body of coating metal Whilesaid portion is molten, said molten portion being out of lateral contactwith physical supporting means, said electromagnetic field beingestablished by coil means disposed about said portion with the axis ofsaid coil means substantially vertical.

8. In a coating process in which coating metal is thermally evaporatedunder vacuum, the steps which comprise establishing a localizedalternating electromagnetic field having a frequency of 5 to 50liilocycles per second energizing an induction heating coil disposedwith its axis substantially vertical, vertically supporting an elongatedbody of coating metal with an end portion of said body projectinggenerally vertically into said coil and being surrounded by said coil,in-

ductively melting said end portion of said elongated body, maintainingsaid alternating electromagnetic field about said end portion andthereby electromagnetically compacting and laterally supporting said endportion in said field while said end portion is molten, said molten endportion being out of lateral contact with physical supporting means,subjecting said molten end portion to vacuum ellective to causesubstantial evaporation of said portion, and progressively advancingsaid elongated body into said coil as said end portion evaporates.

9. The process of continuously coating sheet material which comprisesestablishing in an evacuated space a localized alternatingelectromagnetic field having a frequency of 5 to 50 kilo cycles persecond by energizing an induction heating coil disposed with its axissubstantially vertical, vertically supporting an elongated body ofcoating metal with an end portion of said body extending into saidelectromagnetic field, said end portion being surrounded by said coil,in ductively melting said portion of said body in said field,maintaining said alternating electromagnetic field about said endportion and thereby electromagnetically compacting and supporting saidend portion of said body out of lateral contact with physical supportmeans while said end portion is molten, subjecting said. molten endportion to vacuum effective to cause substantial evaporation of saidportion, passing sheet material to be coated in coating proximity tosaid field, and progressively advancing said body of coating metal intosaid coil during said process.

GEORGE H. BAN C LOFT.

REFERENCES CITED The following references are of record in the fie ofthis patent:

UNITED STATES PATENTS Number Name Date 1,648,962 Rentschler -s lov. 15,1927 2,157,478 Burkharclt ll lay 9, 1939 2,217,228 Macksoud Oct. 8, 19402,239,642 Burkhardt Apr. 22, 1941 2,378,476 Guellich June 19, 19452,411,409 Ballard Nov. 19, 1946 2,459,929 Osterberg May 10, 1949 OTHERREFERENCES 233,455, Berghaus (A. P. C.), May 4, 1943.

